This Small Business Innovation Research (SBIR) Phase I project aims to develop a novel 3-D X-ray imager that will allow potential users to directly obtain 3D images with a single X-ray exposure. Computer Tomography (CT) permits capturing a 3D image of an object however, it requires bulky and expensive mechanical parts to produce a series of 2D X-ray images taken around a single axis of rotation. The proposed imager will overcome these limitations so that 3D X-ray imaging can become as portable and widespread as 2D. The expertise in design of monolithic X-ray imagers that combines high-speed precision electronics for signal processing will be employed. This design will use bulk silicon as a direct photon-to-electron X-ray detector to sense backscattered X-rays. The use of time of flight measurement, 56 ranging bins will ensure high depth resolution. A novel gating feature will permit further increase in resolution and detuning the image of the objects that obscure the target areas. During Phase I a circuit design and in silico validation of the 3D X-ray imager will be provided. During Phase II a monolithic prototype will be designed, fabricated using a commercial silicon technology and tested resulting in a full commercial product. The broader impact/commercial potential of this project includes the ability to manufacture the 3D X-ray imager on 200mm standard CMOS wafers as a wafer scale chip including the X-ray detector array based on direct X-ray photon to electron conversion. The proposed 3D X-ray imager allows for a revolutionary breakthrough in the construction of CT scanners for medical applications, improvised explosive devices (IED) detection for military, luggage and cargo screening equipment. In order to make CT equipment compact, the proposed 3D X-ray imager eliminates mechanical parts. According to industry estimates, the global X-ray imaging sensor market is expected to grow from $700 million or 19,000 units in 2008 to $7.2 billion or 212,000 units in 2012. This new technology will make handheld CT scanning inexpensive. Medical personnel will be able to quickly assess injuries even when they are not close to a standard CT machine as may happen in a remote area, on the battlefield, and at the scene of a natural disaster or terrorist attack. It is expected to sell this device to CT scanner producers, IED detection device manufacturers, and airport luggage and cargo screening equipment manufacturers to replace currently used 2D imagers.